Conventional techniques for manufacturing flat panel displays or semiconductor devices entail applying a sequence of processes to a substrate such as a glass plate or a silicon wafer. The processes to be applied may include thermal processing, physical vapor deposition (PVD), chemical vapor deposition (CVD), etching, etc. Typically, each process in the sequence of processes is performed in a respective processing chamber. Accordingly, the substrates upon which the processes are performed must be transferred from one processing chamber to another.
It is also conventional to incorporate a number of different processing chambers in a single processing tool, wherein the processing chambers are coupled along the periphery of a central transfer chamber. FIG. 1 is a schematic side view of a conventional processing tool 11. The processing tool 11 includes a centrally-positioned transfer chamber 13. A load lock chamber 15 and a processing chamber 17 are shown coupled to respective sides of the transfer chamber 13. One or more additional processing chambers and/or load lock chambers, which are not shown, may also be coupled to respective sides of the transfer chamber 13. The load lock chamber 15 is provided to accommodate introduction of substrates into the processing tool 11 from outside the processing tool 11.
The transfer chamber 13 includes a main body 19 having side walls 21 (of which only two are visible in FIG. 1). Each side wall 21 may be adapted to have a load lock or processing chamber coupled thereto. The transfer chamber 13 also includes a top 23 supported on the main body 19. A lid 25 is provided to sealingly close the top 23 of the transfer chamber 13.
A lower end of the transfer chamber 13 is closed by a substantially annular bottom 27. The bottom 27 of the transfer chamber 13 has a central aperture 29 which accommodates installation of a substrate handling robot 31 in the transfer chamber 13. The substrate handling robot 31 is adapted to transfer substrates among the processing chambers 17 and the load lock chamber or chambers 15 coupled to the transfer chamber 13.
To minimize the possibility of contamination of substrates processed in the processing tool 11, it is customary to maintain a vacuum in the interior of the transfer chamber 13. Hence, the processing tool 11 may be referred to as a vacuum processing system. A pumping system, which is not shown, may be coupled to the transfer chamber 13 to pump the transfer chamber 13 down to a suitable degree of vacuum.
Also illustrated in FIG. 1 is an actuator 33 which selectively opens and closes a slit valve 35 associated with the processing chamber 17. When the slit valve 35 is in an open position (not shown), a substrate may be introduced into or removed from the processing chamber 17. When the slit valve 35 is in the closed position illustrated in FIG. 1, the processing chamber 17 is isolated from the transfer chamber 13 so that a fabrication process may be performed on a substrate within the processing chamber 17.
FIG. 2 is a schematic vertical cross-sectional view showing on a larger scale the slit valve 35 and associated actuator 33 of the processing tool 11. The slit valve 35 is adapted to selectively seal a passage 37 which, when the slit valve 35 is in an open condition (not shown) communicates between the transfer chamber 13 and the processing chamber 17. The passage 37 terminates at a slit-shaped opening 39 on the processing chamber side of the passage 37, and terminates in a slit-shaped opening 41 on the transfer chamber side of the passage 37.
A door seating surface 43 surrounds the opening 41 and may be part of the sidewall 21 of the transfer chamber 13. In accordance with a known practice, the door seating surface 43 defines a plane which is inclined at an angle (e.g., 45°) from a path (indicated by arrow 45) by which a substrate (not shown) is transferred through the passage 37. A slit valve door 47 is mounted on a second end 49 of an actuator shaft 51 that is part of the actuator 33. The slit valve door 47 is adapted to selectively seal against the seating surface 43 so as to gas-tightly isolate the processing chamber 17 from the transfer chamber 13. In particular, the slit valve door 47 may include an O-ring (not separately shown) to form a seal between the slit valve door 47 and the door seating surface 43. The sealing position of the slit valve door 47 is indicated in solid lines in FIG. 2. The actuator 33 is operable to retract the slit valve door 47 to a position shown in phantom and indicated as 53. When the slit valve 47 is in its retracted position 53, the slit valve 35 is in an open condition, and the passage 37 is not obstructed by the slit valve door 47, so that a substrate may be transferred between the transfer chamber 13 and the processing chamber 17.
The conventional slit valve arrangement may also include a bellows (not shown so as to simplify the drawing) which is connected between the second end 49 of the actuator shaft 51 and the bottom 27 of the transfer chamber 13. The bellows may be provided to seal around the actuator shaft 51.
As noted above, it is customary to maintain a vacuum pressure in the transfer chamber 13 during processing operations. A process which may be performed in the processing chamber 17, such as chemical vapor deposition or etching, may call for maintaining a high pressure (e.g., 5 atmospheres) in the processing chamber 17 during processing. In order to maintain isolation between the transfer chamber 13 and the processing chamber 17 while a high pressure process is performed in the processing chamber 17, it is necessary that the slit valve door 47 be held against the sealing surface 43 with a force sufficient to resist the force exerted in an outward direction (i.e., from the processing chamber 17 toward the transfer chamber 13) by the pressurized gas in the processing chamber 17.
As the dimensions of the processing tool 11 are increased to accommodate processing of larger substrates, the size of the slit valve door 47 is increased, and of particular concern in the present instance, the surface area of the slit valve door 47 exposed to the passage 37 is increased. Consequently, the effective force applied by the pressurized gas in the processing chamber 17 against the slit valve door 47 is increased. The increase pressure experienced by the slit valve door 47 leads to a need to increase the force with which the slit valve door 47 is held against the door sealing surface 43. To provide such an increased sealing force, it could be contemplated to increase the size of the actuator 33. However, space considerations may make it impractical to increase the size of the actuator 33. Furthermore, if the slit valve door 47 is pressed against the sealing surface 43 with the increased force (e.g., at a time when the processing chamber 17 is not pressurized), the O-ring which is intended to seal between the slit valve door 47 and the door sealing surface 43 may be compressed to such a degree that metal-to-metal contact may occur between the slit valve door 47 and the door sealing surface 43. Such metal-to-metal contact may generate particles, which may adversely affect the devices processed within the processing tool 11.